Cogeneration, also called combined heat and power (CHP), refers to the use of a power station to deliver two or more useful forms of energy, for example, to generate electricity and heat at the same time. All conventional, fuel-based plants generate heat as by-product, which is often carried away and wasted. Cogeneration captures part of this heat for delivery to consumers and is thus a thermodynamically efficient use of fuel, and contributes to reduction of carbon emissions. This book provides an integrated treatment of cogeneration, including a tour of the available technologies and their features, and how these systems can be analysed and optimised. Topics covered include benefits of cogeneration; cogeneration technologies; electrical engineering aspects; applications of cogeneration; fuels for cogeneration systems; thermodynamic analysis; environmental impacts of cogeneration; reliability and availability; economic analysis of cogeneration systems; regulatory and legal frameworks; selection, integration and operation of cogeneration systems; simulation and optimisation; synthesis, design and operation; examples of cogeneration projects; research and development of cogeneration; summary and conclusions. This book is intended for instructors and students at advanced undergraduate as well as graduate level, for professional engineers who design, build and operate cogeneration systems, and for researchers on analysis and optimisation of energy systems.

The electric and thermal loads at one or more sites (building, industrial unit, etc.) are usually covered by purchasing electricity from the local electricity network and by generating useful heat by burning a fuel in a boiler or a furnace located at the site. However, the production of electricity in a power plant is accompanied by production of heat, which results in a huge waste of energy in case the heat is rejected to the environment via the exhaust gases and the cooling circuits of the plant. Most of this heat can be recovered and used to cover thermal loads, thus converting the power plant to a cogeneration system, which increases the efficiency of fuel use from 40%-50% to 80%-90%. Many definitions of cogeneration (called also Combined Heat and Power) have appeared in legislature and in the general literature. The following one is proposed here: Cogeneration is the simultaneous generation of work and useful heat from the same primary energy source.

The substantial growth in wealth level in the world since the beginning of the twentieth century is primarily based on energy use. Fossil fuels feed the machines and processes that enable a tremendous productivity growth and supply of consumption articles. A modern diesel tractor is at least by a factor 1,000 more powerful than a human labourer with a spade. Nitrogen fertiliser is produced with fossil fuel and drastically enhances agricultural productivity. Containerships with a propulsion power of up to 90 MW and aeroplanes with up to 140-MW jet power enable global trading and travel. Electricity allows easy communication and offers tremendous calculating power with computers. Air conditioning facilitates comfortable living in otherwise uninhabitable climates and refrigeration makes long-time storage of food possible. So far, energy has been very affordable compared with the benefits it offers. Consequently, energy consumption has increased at a speed as if the resources would be infinite. People in the deprived regions of the world can only be lifted out of poverty by offering them affordable energy. Fear of depletion of the cheap-fuel resources coupled with increasing anxiety of excessive global warming have led to advocate cogeneration of heat and electricity and to support for a drastic increase in renewable energy. This section will describe the relationship between energy use and the global economy.

This chapter gives an overview of the available cogeneration technologies and their performance. The basis of cogeneration is always that the bulk of the heat released during a process of converting fuel energy into mechanical or electrical energy is not wasted but economically used. The machine that converts the fuel into mechanical energy and heat is often called the prime mover. Common prime movers are gas turbines, reciprocating engines and more recently also fuel cells. Mechanical energy can be converted into electrical energy with an electric generator, whereas heat can be transformed into chill with an absorption chiller. Heat exchangers are an integral part of cogeneration installations. Heat pumps are also increasingly used in such installations.

This chapter will describe the electrical system in a cogeneration plant. The general set-up will be described in this section. The various generator types are described in the paper. The system interconnection and aspects of control and stability, active power control, and reactive power are also described.

This chapter discusses: Introduction to applications of cogeneration; Cogeneration in the utility sector; Cogeneration in the industrial sector; Cogeneration in the commercial sector; Cogeneration in the agricultural sector; and Cogeneration in combination with renewable energy.

This chapter will highlight the properties of fuels of interest for cogeneration systems and discuss the consequences for the combustion process and the emissions. The fuel properties partly determine the fuel efficiency and the emissions. Also combustion velocity and combustion stability are important issues. Examples of typical fuel properties are the volumetric or mass-based heating value and the minimum specific air requirement for complete combustion. The ignition range and autoignition properties are other properties of interest. Exceeding the fuel quality range for which the process has been tuned can introduce serious safety and performance issues. There is a direct relationship between the fuel composition and the carbon dioxide (CO2) emissions, but also other undesirable combustion end products depend on the fuel composition.

The purpose of this chapter is to provide the means for evaluation of the performance of cogeneration and trigeneration systems from the point of view of useful energy products, primary energy consumption and primary energy savings. The correct definition and calculation of efficiencies and the primary energy savings are important in order not only to obtain a clear picture of what cogeneration can achieve but also to reveal whether a particular system is eligible for economic incentives provided in several countries for promotion of cogeneration, such as subsidy on investment, guaranties of origin and special tariff for electricity coming from high efficiency cogeneration. A cogeneration system may operate at a variety of loads and external conditions. Thus, an analysis on the design point only may lead to overestimation of its thermodynamic performance. If these results are then used for evaluation of its economic performance, they may give a wrong picture of the economic viability of the investment. For this reason, an example with off-design performance will also be presented in this chapter.

Application of cogeneration may have both positive and negative effects on depletion of non-renewable energy resources, on the environment, and on the society. Environmental effects, in particular, can be distinguished in effects on air, water, and soil quality, as well as on noise and vibration. Since cogeneration increases the efficiency of fuel utilization, it can lead to decreased emission of pollutants to the environment. Furthermore, since the whole fuel cycle includes steps such as exploration, extraction, refining, processing, transportation, and storage, not only the direct emissions from the use (burning) of fuel, but also the emissions of the whole fuel cycle can be decreased. However, depending on the cogeneration technology and the fuel used, it is possible that certain emissions may increase with cogeneration.

This chapter will first discuss the definitions of the relevant quantities. These definitions depend to some extent on the nature of a product and the specific demands of the user. In addition, based on the definitions, a methodology is given to express reliability and availability in terms of numbers. Further, this chapter provides the statistical background to determine the required redundancy to reach the desired output reliability. That helps to define the optimum maintenance philosophy and the amount of reserve capacity.

Cogeneration systems are capital-intensive installations. Even if a cogeneration system has high-energy efficiency, it will not be possible to proceed with the investment unless it is also economically viable. The procedure for evaluation of the economic performance of cogeneration systems is presented in this chapter, supported with information about the various types of costs, definition of the most important of the economic parameters and measures used for evaluation, as well as examples of economic analysis. Two additional issues are also tackled: (a) the distribution of costs of a cogeneration system among its energy products and (b) the effect of the internalization of environmental externalities on the cost of covering energy needs either by a cogeneration system or by the conventional approach, that is separate production of work and heat. Care has been exercised so that the values of costs given here to be realistic. However, they can be considered indicative only, as they change with place and time. Consequently, the economic performance evaluation of any cogeneration project should be based on cost information obtained for the particular project.

This chapter presents the regulatory and legal framework of cogeneration. It is known that the first commercial combined heat and power (CHP) unit started its operation in 1882, in New York, United States, producing both electrical and thermal energy using waste heat, in order to heat nearby buildings, operating in a nonregulatory environment. But in the late 1800s, new regulations were enacted in the United States of America to promote rural electrification, by constructing centralised power plants, which discouraged decentralised ones, like those for cogeneration.

This section will highlight a series of common problems experienced during integration of cogeneration systems. Even after extensive design efforts and simulations, problems do occur at the implementation stage or during occasional unusual situations at the user side, sometimes caused by human error. An interesting summary of such situations, including solutions, is found in [1], which is unfortunately only available in Dutch. The lack of much international literature on the subject is caused by the fact that most problems occurring are typically solved by plumbing engineering rather than by a scientific approach. Much knowledge exists at dedicated installers of combined heat and power (CHP), but such organisations do not often publish their results.

In Chapters 7, 8 and 10, indexes have been defined and procedures have been described for evaluation of cogeneration systems from the point of view of thermodynamic, environmental and economic performance, respectively. In order to perform this evaluation, there is need either to measure or to compute certain operating parameters such as electrical, mechanical and thermal energy produced, pollutants emitted, fuel consumption and various costs in a certain period of time. In order to compute these parameters, there is need to construct the simulation model of the system, which consists of a set of equations that describe the performance of the system by mathematical terms. The simulation model is also a prerequisite for optimisation of the system, that is for determining the best structure, nominal (design) specifications and operating point of the system at each instant of time, taking into consideration the technical and economic conditions prevailing at this instant. The development of simulation models and the optimisation of the synthesis (structure), design and operation of cogeneration systems are the subjects of this chapter.

The scope of this chapter is to present successful cogeneration projects. As written in Chapter 5, there are four main sectors of cogeneration applications: utility, industrial, commercial (called also building), and agricultural sector; district heating can be categorized in the utility sector. Therefore, the example projects will be presented in the following by the application sector. Undoubtedly, there are innumerable successful cogeneration projects worldwide, and the intention here is not to give an exhaustive list (it would be rather impossible) but to give only a few characteristic examples. The selection was necessarily restricted to combined heat and power (CHP) plants with data available in the open literature only, so that revealing proprietary information is avoided. The eight applications of cogeneration, presented in this chapter, are covering all types of technologies (i.e., internal combustion engines, combined cycle, steam turbine, gas turbine, etc.), all major fuels used (i.e., natural gas, biomass, coal, etc.), all various capacities (i.e., micro, small-scale, and large), and all sectors of the economy (i.e., utility, industrial, commercial, and agricultural), so that the reader can form an integrated overview and understanding of modern cogeneration projects.

Cogeneration has been applied for more than a century and, consequently, it can be considered a mature technology. However, new challenges, such as increased awareness of the depletion of fuels and other natural resources, the pollution of the environment beyond acceptable limits and the scarcity of water in many areas on earth, give the impetus for a continuous research and development (R&D) on cogeneration systems. Samples of this activity are given in this chapter, arranged by the focus subjects of R&D. The reference list cannot be exhaustive; it is indicative only.

It was recognized in the 1970s and beyond that cogeneration can be a strong instrument in primary energy savings and in reducing CO2 and other emissions. Thus, promotion of cogeneration has been one of the goals in energy policy and for this purpose, special laws and regulations started being issued, first in the United States of America and then in other countries worldwide as well as in the European Union. Also, the International Energy Agency in Paris recommends cogeneration as an effective means to reduce fossil fuel consumption. Among other subjects, rules for the cogeneration systems to be eligible for financial and economic incentives have been issued, as well as for their participation in the electricity market. The gap between the fuel and electricity price affects crucially the economic viability of cogeneration. Furthermore, it is noted that cogeneration may have difficulty in penetrating both `close-to-slow-opening' and fully liberalized electricity markets. Thus, the regulatory and legal framework needs to be updated from time to time.